Initiator and gas generator

ABSTRACT

An initiator includes a casing, a reactant disposed in the casing, and electrodes arranged to contact the reactant. The reactant contains an electrically conductive substance in a manner such that once a voltage is applied to the electrodes, an electric current flows through the electrically conductive substance, thereby initiating a reaction of the reactant. The initiator is easily manufactured with low manufacturing cost.

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to an initiator suitable forinstalling in a gas generator of an airbag apparatus and a seat beltpre-tensioner. This invention also relates to a gas generator equippedwith such an initiator.

[0002] An airbag apparatus provided in a fast moving vehicle such as anautomobile is usually constructed in a manner such that a gas generatorcalled an inflator quickly inflates a bag-shape airbag. Such a gasgenerator comprises a gas generating agent and an initiator forinitiating a reaction of the gas generating agent. Conventionally, suchan initiator comprises a reactant and a filament (a bridge wire) servingas a resistive heating element for initiating the reaction of thereactant.

[0003] An example of a conventional initiator will be described belowwith reference to FIG. 8.

[0004] An initiator 10 includes a substantially cap-shape casing 12having an opening at a rear portion (a lower portion in FIG. 8). Areactant 14 is stored in the casing 12. An insulator 16 such as asintered glass and the like seals the rear portion of the casing 12. Apair of electrodes 18, 20 is penetrating through the insulator 16 sothat end portions thereof are exposed in the interior of the casing 12.

[0005] A filament 22 is bridged between the end portions of the twoelectrodes 18 and 20. Both ends of the filament 22 are welded tosurfaces of the end portions of the respective electrodes 18 and 20.Further, the filament 22 is in contact with the reactant 14 in thecasing 12.

[0006] The two electrodes 18, 20 and the casing 12 are arrangedseparately from each other so that they are not electrically connectedwith each other.

[0007] In the initiator 10 constructed in the above-described manner,the electrode 18 is connected to a positive electrode of an automobilebattery 26 through a control circuit 24 equipped with a voltage step-upcircuit and the like, while the other electrode 20 is connected (earthconnection) to a main body of an automobile. A negative electrode of thebattery 26 is connected to the main body of an automobile.

[0008] In a case of an accident such as a collision between automobilesand the like, a switching element within the control circuit 24 turnson, so that a voltage from the battery 26 is applied to the filament 22through the respective electrodes 18 and 20. As a result, the filament22 generates heat to ignite the reactant 14, thereby initiating thereaction of the reactant. The reaction of the reactant 14 generates ahigh-pressure gas and a large amount of heat, so that the gas generatingagent in the gas generator initiates a gas generating reaction.

[0009] The reactant includes, for example, the first reactant and thesecond reactant. The first reactant is arranged around the filament 22and is a mixture of a lead styphnate and an aluminum powder. The secondreactant is arranged around the first reactant and consists of BKNO₃ ora black powder. The first reactant quickly undergoes a heat generatingreaction, while the second reactant starts its reaction by virtue ofheat produced by the first reactant, thereby generating a high-pressurehot gas as well as fine particles.

[0010] An example of a conventional gas generator equipped with theinitiator 10 is described as follows with reference to FIG. 9. Aconventional gas generator 30 includes a container having an outer caseconsisting of an upper housing 32 and a lower housing 34, and having acylindrical partition member 36 disposed within the outer case. One endof the cylindrical partition member 36 protrudes downwardly through anopening formed at the bottom of the lower housing 34. An internalcircumferential surface of the opening and an external circumferentialsurface of the cylindrical partition member 36 are welded together bymeans of laser beam welding and the like. An igniting agent (boosterpropellant) 40 is stored in the cylindrical partition member 36, while agas generating agent (main propellant) 42 is arranged at an outside ofthe cylindrical partition member 36.

[0011] As shown in the drawing, the initiator 10 is disposed at one endof the cylindrical partition member 36. When the igniting agent 40 isignited by the initiator 10, a gas erupts through openings 44 of thecylindrical partition member 36, thus igniting the gas generating agent42. As a result, a large amount of gas is generated rapidly, passingthrough filters 46 consisting of meshes and the like, and furtherpassing through openings 48. Consequently, the gas erupts out of the gasgenerator 30, thereby inflating an airbag. Note that FIG. 9 shows onlyone example of the conventional gas generators, and there are many typesof gas generators having shapes different from that shown in thedrawing.

[0012] In the conventional initiator shown in FIG. 8, in order to ensurea predetermined constant electric resistance of the filament 22, amanufacturing process is required to perform a strict control on alength of the filament 22 as well as a welding condition when connectingthe same. As a result, it is difficult to reduce time and labor in themanufacturing process, hence making it difficult to reduce a productioncost.

[0013] Accordingly, it is an object of the present invention to providean improved initiator without using a resistive heat generator such as afilament and the like, and can be manufactured easily and thus at areduced cost.

[0014] It is another object of the invention to provide an improved gasgenerator equipped with such an improved initiator.

[0015] Further objects and advantages of the invention will be apparentfrom the following description of the invention.

SUMMARY OF THE INVENTION

[0016] An initiator of the present invention comprises a casing, areactant disposed in the casing, and electrodes arranged to contact thereactant. The reactant contains an electrically conductive substance ina manner such that once a voltage is applied to the electrodes, anelectric current flows through the electrically conductive substance,thereby initiating a reaction of the reactant.

[0017] In the initiator of the present invention, once a voltage isapplied to the electrodes, an electric current will flow between theelectrodes through the electrically conductive substance containedwithin the reactant, thereby causing the electrically conductivesubstance to produce heat. This heat initiates the reaction of thereactant, thereby generating a high-pressure gas and heat to ignite agas generating agent in a gas generator. The initiator contains theelectrically conductive substance instead of using a filament, thus itis possible to simplify a manufacturing process, resulting in a uniformquality, a higher yield and a lower cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIGS. 1(a) and 1(b) are cross sectional views showing aninitiator according to an embodiment of the present invention;

[0019]FIG. 2 is a cross sectional view showing an initiator according toan embodiment of the present invention;

[0020]FIG. 3 is a cross sectional view showing an initiator according toan embodiment of the present invention;

[0021]FIG. 4 is a cross sectional view showing an initiator according toan embodiment of the present invention;

[0022]FIG. 5 is a cross sectional view showing an initiator according toan embodiment of the present invention;

[0023]FIG. 6 is a cross sectional view showing an initiator according toan embodiment of the present invention;

[0024]FIG. 7 is a cross sectional view showing an initiator according toan embodiment of the present invention;

[0025]FIG. 8 is a cross sectional view showing a conventional initiator;

[0026]FIG. 9 is a cross sectional view showing an example of aconventional gas generator;

[0027]FIG. 10 is a cross sectional view showing an initiator accordingto an embodiment of the present invention; and

[0028]FIG. 11 is a cross sectional view showing an initiator accordingto an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0029] Hereunder, embodiments of the present invention will be describedwith reference to the accompanying drawings. FIG. 1 to FIG. 7 are crosssectional views showing initiators according to the embodiments of thepresent invention.

[0030] In FIG. 1(a), an initiator 50 has a casing 56 including a cup 52and a head 54 inserted in the cup 52 through its opening. The casing 56is filled with a reactant 58. In the present embodiment, the cup 52 is acircular container formed of SUS 304 or the like. The head 54 is asubstantially circular member also formed of SUS 304 or the like. Anouter circumference surface of the head 54 is secured onto the innercircumference surface of the cup 52 by welding and the like.

[0031] An internal space is formed between a front surface of the head54 and a bottom surface of the cup 52, while the reactant 58 is receivedin the internal space.

[0032] A through hole 60 is formed through a central portion of the head54 in a thickness direction thereof. An electrode pin 62 is inserted inthe through hole 60 and is secured in the head 54 by means of aninsulating securing material 64 such as a glass and the like. Further,in the present embodiment, the front-end surface of the pin 62 is at thesame height as that of the front-end surface of the head 54. Moreover,another electrode pin 66 is secured by welding and the like on the rearend surface of the head 54.

[0033] The outer surface of the cup 52 is covered by a resin cover 68formed of nylon, polypropylene or the like. The rear portion of the cup52 as well as the rear end surface of the head 54 are covered by a resincover 70 formed of nylon, polybutylene terephthalate or the like. Bothpins 62 and 66 are arranged to protrude outwardly through the resincover 70.

[0034] The reactant 58 contains a reactive component such as a valvemetal like Al, Ti and the like having a rectifying function, andelectrically conductive particles 58 a. The electrically conductiveparticles 58 a include metal particles and/or metal oxide particles. Themetal particles include aluminum particles, magnesium particles,tantalum particles, zirconium particles, copper particles, or the like.

[0035] The metal oxide particles include oxide particles such as Ti₂O₃particles, MoO₂ particles, MnO₂ particles or the like, each of which hasan electrical conductivity and can also function as an oxidant.Preferably, the specific resistance of the electrically conductive metaloxide particles is equal to or less than 0.1 Ωm. The reactant maycontain both metal particles and electrically conductive oxideparticles.

[0036] Further, the reactant may contain non-conductive oxidantparticles. For example, it is possible for the reactant to contain bothmetal particles and non-conductive oxidant particles.

[0037] In the initiator 50 having the above-described structure, once avoltage is applied between the pins 62 and 66, an electric current willflow between the pin 62 and the head 54 through the electricallyconductive particles 58 a contained in the reactant 58. Then, due toJoule heat generated by the electric current flowing therethrough, thereactant 58 starts to react, thus producing a high-pressure gascontaining hot particles. At this time, in the case that the reactant 58contains the oxidant particles, the reaction may be accelerated due toan oxidization action produced by the oxidant particles. In the casethat the electrically conductive particles 58 a contains both theelectrically conductive oxidant particles and metal particles, theelectrically conductive oxidant shows the oxidation activity during theexothermic process, thereby causing the metal particles to be quicklyoxidized and thus producing the heat.

[0038] In the present embodiment, since a filament (wire bridge) is notused, it is possible to greatly reduce a manufacturing cost.

[0039] In FIG. 1(a), the front-end surface of the pin 62 is located atthe same height as that of the front-end surface of the head 54.However, it is also possible that the front end of a pin 62′ projectsbeyond the head 54 so as to extend into the reactant 58, as in anotherinitiator 50′ shown in FIG. 1(b). In this way, it is possible toincrease a contact area between the pin 62′ and the electricallyconductive particles 58 a dispersed in the reactant 58. Since otherportions and elements of the initiator 50′ shown in FIG. 1(b) are thesame as those of the initiator 50 shown in FIG. 1(a), the same portionsand elements are represented by the same reference numerals.

[0040] An initiator 50A shown in FIG. 2 has a pin 62A formed of a frontportion 62 a and a rear portion 62 b connected with each other by meansof welding. The front portion 62 a of the pin is integrally connected inadvance with a solid electrically conductive oxidant 72. The frontportion 62 a of the pin is inserted through the hole 60 of the head 54and welded to the rear portion 62 b of the pin. A reference number 62 wrepresents a welded position. The solid electrically conductive oxidant72 is surrounded by a surrounding material 74. The surrounding material74 is formed of a metal. Since other portions and elements of thisinitiator are the same as those of the initiator 50 shown in FIG. 1(a),the same portions and elements are represented by the same referencenumerals.

[0041] An initiator 50B shown in FIG. 3 employs a casing including a cup76 formed of a synthetic resin and a plug 78 formed of a syntheticresin. The casing is filled with the reactant 58 containing metalparticles 80 and electrically conductive oxide particles 82. The pins 62and 66 pass through a resin cover 70 and a plug 78, and protrude intothe reactant 58. It is also possible to use non-conductive oxideparticles instead of the electrically conductive oxide particles 82.

[0042] In an initiator 50C shown in FIG. 4, a metal block 84 is fixed tothe front end of the pin 66 of the initiator 50B shown in FIG. 3. Thereactant 58 contains the electrically conductive oxide particles 82, anddoes not contain metal particles.

[0043] In an initiator 50D shown in FIG. 5, a box-like casing 86 made ofa synthetic resin contains the reactant 58. As shown in the drawing, ametal cup 88 is provided along a side surface as well as a bottom faceof the casing 86. The metal cup 88 electrically contacts the pin 66. Thereactant 58 contains only the electrically conductive oxide particles82, and does not contain metal particles.

[0044] In initiators 50C′ and 50D′ shown respectively in FIG. 6 and FIG.7, the metal block 84 and the metal cup 88 of the initiators 50C and 50Dshown in FIG. 4 and FIG. 5 are covered by oxidized films 90 and 92,respectively, thereby adjusting an electric resistance between the pins62 and 66. Here, although the oxidized film 92 is provided on an innersurface of the metal cup 88 and an outer surface of the pin 66, theoxidized film 92 is not provided on an interface between the metal cup88 and the pin 66.

[0045] When a voltage is applied between the pins 62 and 66, theoxidized films 90 and 92 is broken, thereby generating additional heat.

[0046] In initiators 5OC″ and 50C′″ shown respectively in FIG. 10 andFIG. 11, an electrically conductive oxide block 96 is used instead ofthe reactant 58 and the electrically conductive particles 58 a of theinitiators 50C and 50C′ shown in FIG. 4 and FIG. 6, thereby simplifyinghandling and a manufacturing process.

[0047] In the present invention, the aforementioned metal block, metalcup as well as the electrically conductive oxides may have a poroussurface. By virtue of such a porous surface, it is possible to improvereaction sensitivity.

[0048] The reactant containing the metal particles and electricallyconductive oxidant particles is preferable to have a composition notlisted in the powder list of Active Carbon Regulation.

[0049] Each of the above-described embodiments is only an example of thepresent invention. The present invention is also allowed to have anembodiment other than those illustrated in the accompanying drawings.For example, the casing is allowed to have a shape other than thoseillustrated in the drawings. Similarly, the shape and the number of theelectrodes are not limited to those shown in the accompanying drawings.The casing may have a long and narrow cylindrical shape so that it canbe used in a gas generator of an airbag apparatus for a passenger seat.

[0050] The initiator of the present invention can be applied to varioustypes of gas generator. The initiator can be incorporated into varioustypes of an airbag apparatus and a seat belt tensioner for a driverseat, a passenger seat, a rear seat, a side portion and a head portionof a person's body, as well as for protecting pedestrians.

[0051] As described above, in the initiator according to the presentinvention, since a bridge wire is not used, it is possible to eliminatea welding step during the manufacturing process, thereby making itpossible to provide an improved initiator easy to be manufactured andlow in the manufacturing cost, as well as an improved gas generatorequipped with such an improved initiator.

[0052] While the invention has been explained with reference to thespecific embodiments of the invention, the explanation is illustrativeand the invention is limited only to the appended claims.

What is claimed is:
 1. An initiator, comprising: a casing, a reactantdisposed in the casing and containing an electrically conductivesubstance, and electrodes situated inside the casing to contact thereactant such that when a voltage is applied to the electrodes, anelectric current flows through the electrically conductive substances,thereby initiating a reaction of the reactant.
 2. An initiator accordingto claim 1, wherein said electrically conductive substance includes atleast ones of metal particles and metal oxide particles.
 3. An initiatoraccording to claim 1, wherein said reactant contains metal oxideparticles having oxidization activity and metal particles havingelectrical conductivity.
 4. An initiator according to claim 1, whereinsaid electrodes are pin members having front-end portions extending intothe reactant.
 5. An initiator according to claim 1, further comprising ametal member electrically connected to one of the electrodes andcontacting the reactant.
 6. An initiator according to claim 5, furthercomprising an oxidized film covering the metal member.
 7. An initiatoraccording to claim 5, wherein said metal member has a porous surface toimprove reaction response.
 8. An initiator according to claim 5, furthercomprising a pre-assembled block formed of the reactant connected to theother of the electrodes.
 9. An initiator according to claim 8, whereinsaid pre-assembled block further includes a surrounding materialcovering the reactant, said metal member contacting the surroundingmaterial.
 10. A gas generator comprising the initiator according toclaim 1, and a gas generating agent to be ignited by the initiator forgenerating a gas.